Assessing causal links in fish stock–recruitment relationships

Abstract

Understanding whether recruitment fluctuations in fish stock arise from stochastic forcing (e.g. environmental variations) rather than deterministic forces (e.g. intrinsic dynamics) is a long standing question with important applied consequences for fisheries ecology. In particular, the relationship between recruitment, spawning stock biomass and environmental factors is still poorly understood, even though this aspect is crucial for fisheries management. Fisheries data are often short, but arise from complex dynamical systems with a high degree of stochastic forcing, which are difficult to capture through classic modelling approaches. In the present study, recent statistical approaches based on the approximation of the attractors of dynamical systems are applied on a large dataset of time series to assess (i) the directionality of potential causal relationships between recruitment and spawning stock biomass and potential influence of sea-surface temperature on recruitment and (ii) their performance to forecast recruitment. Our study shows that (i) whereas spawning stock biomass and sea surface temperature influence the recruitment to a lesser extent, recruitment causes also parental stock size and (ii) that non-linear forecasting methods performed well for the short-term predictions of recruitment time series. Our results underline that the complex and stochastic nature of the processes characterizing recruitment are unlikely to be captured by classical stock–recruitment relationships, but that non-linear forecasting methods provide interesting perspectives in that respect.

Nonlinear dynamics and noise in fisheries recruitment: A global meta‐analysis

“…In keeping with earlier results by Pierre et al. (), we find that causal coupling between stock and recruitment is fairly common (Figure ). CCM identified significant causal coupling between stock size and recruits for 107 of the 185 time series tested (Figure ).…”

“…Previous analyses based on S‐map (e.g. Deyle et al., ; Pierre et al., ) use a fixed lag for each coordinate. In particular, the time step was set to one and all lags up to E are included in the model.…”

“…If this is the case, then fishing—which clearly affects current population size—can have very little influence on the long‐term dynamics of harvested populations. Moreover, as fisheries management attempts to maximize production by manipulating fishing effort, the question of whether or not population size and recruitment are causally coupled is highly relevant (Pierre, Rouyer, Bonhommeau, & Fromentin, ). But how best to predict recruitment and identify its causal drivers in the face of considerable empirical complexity is unclear.…”

“…Pierre et al. () recently addressed the question of whether stock biomass and recruitment are causally coupled, by applying convergent cross‐mapping (CCM, Sugihara et al., ) to 53 time series of stock and recruits. They found that although stock size and recruitment were often coupled, stock size did not contribute much to prediction accuracy.…”

Density dependence in total egg production per spawner for marine fish

“…If the density dependence in the spawner-recruitment relationships relies on a masked density dependence in TEPPS/TEPPSW, the TEP-recruitment relationships will be weaker than the SSB-recruitment relationships. Another controversial issue is the relative roles of density-dependent (self-regulating) and density-independent (environmentally regulating) processes throughout the life stages (Andersen et al, 2017;Minto et al, 2008;Myers & Barrowman, 1996;Pierre, Rouyer, Bonhommeau, & Fromentin, 2018). Recent meta-analyses showed that the spawner-recruitment relationships were weaker than previously recognized (Cury et al, 2014;Munch, Giron-Nava, & Sugihara, 2018;Szuwalski et al, 2015).…”